We don't have anything to go on right now, save the image you see here. But previous California Special versions were limited to things like new wheels, spoilers, badges, and some paint options, so we aren't expecting anything too drastic. It's also unclear if Ford will offer the new GT/CS on both the coupe and convertible, or if it'll just stick to the hardtop.
We'll get the full details on Monday, May 11 – that's when Ford will reveal everything it's done for the 2016 Mustang lineup. Stay tuned.